IP multicast refers to sending of a data package with best effort (Best Effort) in an IP network to a certain determined node subset in the network. This subset is referred to as a multicast group (Multicast Group). A basic concept of the IP multicast is that a source host sends only one copy of data, where a destination address in the copy of data is an address of the multicast group and all receivers in the multicast group can receive the same copy of data.
A multicast flow is forwarded along an established multicast forwarding route. A router on the forwarding route may need to forward a message received from one incoming interface to multiple outgoing interfaces in order to transmit a multicast message to a receiving station at each position. A PIM (Protocol Independent Multicast, protocol independent multicast) protocol is a most widely used protocol among protocols for establishing a multicast forwarding route.
A current network service imposes an increasingly higher requirement on a real-time characteristic. When a link fails, a multicast service also needs to reduce a lost multicast data message. The PIM Dual Join (PIM dual join) technology is used to solve a problem that a multicast service is able to converge rapidly when a link fails on a multicast forwarding route. In a PIM Dual Join solution, two forwarding routes for forwarding multicast data are established by applying the same copy of multicast data stream from two directions. When one of links fails, multicast data may be received selectively from a backup multicast forwarding tree.
In an existing multicast PIM protocol, an RPF (Reverse Path Forwarding, reverse path forwarding) rule is a basic rule of multicast, which considers that a multicast entry has merely one upstream, namely, an outgoing interface and a next hop of an optimal unicast routing to a multicast source or a reverse path. The outgoing interface is an RPF interface in the PIM protocol and the next hop is an RPF neighbor in the PIM protocol.
As regards this, the inventor finds that after the PIM Dual Join solution is proposed, a scenario that is not defined in an existing PIM protocol is added. Namely, a PIM protocol entry has two incoming interfaces, which are respectively referred to as a main incoming interface and a backup incoming interface. A behavior of the main incoming interface has been defined in detail in an existing protocol, but the backup incoming interface has a unique peculiarity. The backup incoming interface not only has a property of an incoming interface, but also may exist as an outgoing interface at the same time. Forwarding and protocol behaviors of the backup incoming interface are not defined at present. In this way, compatibility in various manufacturers is not easily implemented, and a restriction of a network topology on the application of the PIM protocol is increased.